1. Field on the Invention
The present invention relates to anti-reflection film, production of anti-reflection film, and multi-layer film producing apparatus. More particularly, the present invention relates to anti-reflection film, production of anti-reflection film, and multi-layer film producing apparatus, in which the production can be easy and also rigidity and workability of the product can be ensured.
2. Description Related to the Prior Art
Anti-reflection film is provided in several sorts of image display devices, such as a liquid crystal display (LCD), a plasma display panel (PDP), an electro luminescence display (ELD), a cathode-ray tube (CRT) and the like. The anti-reflection film is used for an eyeglass, of a lens incorporated in a camera. Several types of the anti-reflection films have a multi-layer structure or a nonuniform layer structure, and are widely used. A film support is provided with a plurality of transparent layers of metal oxides, so as to prevent the reflection in a wide wavelength range of a visible ray.
Such transparent layers of metal oxides are usually formed in methods of vapor deposition. As the methods, there are chemical vapor deposition (CVD) and physical vapor deposition (PVD). Specifically in the PVD, some substances are evaporated, such that a gas thereof in form of molecules or atoms forms a thin layer. The PVD is often made in vacuum deposition method and sputtering method. However, those are unsuitable for mass production, due to difficulties in increasing productivity.
In production of the anti-reflection film, the PVD is often carried out on a film support, while a metal layer on the film support is provided with the protruding and retreating surface pattern in accordance with the way of use. In this type of the anti-reflection film, parallel transmittance becomes lower than in the anti-reflection film having a smooth surface on which that vapor deposition is performed. As the protruding and retreating surface pattern scatters the external light to suppress mirroring, the produced anti-reflection film has antiglare property. Accordingly, such anti-reflection films improve the display quality of the image display device.
Instead of the methods of vapor deposition, the following publications propose methods of producing the anti-reflection film by coating a film support with a solution containing inorganic micro particles for forming an anti-reflection layer: JP-B 60-059250 (corresponding to JP-A 56-084729) and JP-A 59-050401. In JP-B 60-059250, a solution is cast on a film support to form an anti-reflection layer including inorganic micro particles and micro voids. After the solution is dried and forms an anti-reflection layer on the film support, it is processed in gas activation. Thereby, a gas releases from the coating layer, and the micro voids are formed in the coating layer. JP-A 59-050401 discloses a multi-layer structure having a support, a high-refractive-index layer and a low-refractive-index layer overlaid on the former and formed from coating of polymer or inorganic micro particles. In addition, the document suggests provision of a middle-refractive-index layer disposed between the support and the high-refractive-index layer.
JP-A 2-245702 discloses anti-reflection film in which micro particles of two or more compounds, such as MgF2 and SiO2, are contained, and a proportion of mixture of those is changed in the thickness direction of the film. According to JP-A 2-245702, the change in the proportion of the compounds for the particles is effective in changing the refraction index within the film, to obtain a similar optical effect to that of JP-A 59-050401 disclosing the high and low-refractive-index layers in the dual layer structure.
JP-A 5-013021 teaches the improvement of the anti-reflection film of JP-A 2-245702. In the improvement, the micro voids are filled with binder. Further, JP-A 7-048527 teaches anti-reflection film containing binder and inorganic particles of porous silica. Furthermore, JP-A 11-006902 discloses a three-layer structure of film in which a low-refractive-index layer is overlaid on a support and includes plural inorganic micro particles together with micro voids, and coated with coatings in a wet manner. This is characterized in application of all the coatings in the wet manner at a reduced manufacturing cost, and has an intention of strengthening the film even with a lowered reflection.
To impart antiglare properties to the anti-reflection film, various methods are known, including application of a coating an anti-reflection layer to an initially roughened support with a protruding and retreating pattern. Another method is to add mat particles to coating solution for an anti-reflection layer in order to form a protruding and retreating surface pattern. JP-A 2000-275401 and 2000-275404 propose improvements of the anti-reflection films in JP-A 11-006902. At first, a flat anti-reflection film is produced, and a surface thereof is embossed to form the protruding and retreating surface pattern.
In the antiglare film or anti-reflection film, to keep resistance to outer force high, it is conceivable to raise smoothness of the surface by lowering friction or surface energy of the surface, or to raise force of bonds between the plural layers overlaid on one another for high resistance against being peeled. However, it is basically necessary to add at least one hard coat layer which has a characteristically high hardness sufficient for being resistant to outer force.
Documents such as JP-A 6-018704, JP-A 7-027902 and JP-A 2003-311911 disclose dual curing of a coating solution for a hard coat layer. The support is coated with the coating solution, which is cured only for half curing. Then the support is coated with the coating solution for a second time, before the coating solution is dried and then cured completely. In general, there are two types of the dual curing in such known techniques.
Type 1. Curable resin curable with actinic radiation is contained in the coating solution prepared for the hard coat layer. Curing of the curable resin is interrupted for half curing in a state short of the complete curing.
Type 2. Mixture of the curable resin curable with actinic radiation and thermoset resin is contained in the coating solution prepared for the hard coat layer. The support is coated with the mixture, and dried, and either cured or cross-linked by application of either heat or the actinic radiation which may be ultraviolet rays or electron rays.
However, coated polymer film or anti-reflection film having such a hard layer has problems, for example, in a producing line, suitability for handling, or the like.
In a coating apparatus in which a long support is unwound from a roll, continuously advanced, coated and then wound, uneven shape of a cut end surface or dust or powder of cutting are created in various manners, for example, at a cutter used for the splicing of a trailing end of a first strip with a leading end of a second strip of the long support, or at a cutter before winding to the bobbin, or a slitter for cutting away a knurled portion in the case of providing the long support with the knurled portion on each of web edges. Note that the cutter used for the splicing is disclosed in U.S. Pat. No. 4,234,265 (corresponding to JP-B 60-050693) and JP-B 4-078543 (corresponding to JP-A 61-119555). The cutter before winding to the bobbin is disclosed in JP-B 7-033198 (corresponding to JP-A 63-288856).
Also, embossing to a very hard coated surface may cause failure in view of production with good quality. Even after the anti-reflection film is obtained, it is likely that an embosser cannot emboss the coated surface typically when pencil hardness of the hard coat layer is 2H or harder. There will occur accidental breakage of the hard coat layer.
However, it is impossible in the known techniques of the half curing of the above documents JP-A 6-018704, JP-A 7-027902 and JP-A 2003-311911 to control the cured state precisely. For example, adjustment of an application amount of the actinic radiation is to control the amount and distribution of a radical within a coating because the actinic radiation causes the radical to generate. However, the actinic radiation is absorbed by ingredients of the hard coat layer, and diminished in the thickness direction of the coating or direction of transmission of the actinic radiation. Curing is quick on the coated surface but slow at point within the coating with low reaction. It is difficult to control residual cross-linkable ingredient which remains on an uppermost layer of the hard coat layer and is applied for adhesion to the anti-reflection layer.
In the method of blending the thermoset resin with the curable resin curable with the actinic radiation for the hard coat layer, control of both thermosetting is extremely difficult. Heat is applied for the purpose ov evaporating solvent after the coating of the hard coat layer, for example by blowing of hot gas, induction heating with microwaves, or by radiation heating of an infrared heater. However, thermosetting cannot easily suppressed only by controlling the temperature of the coating. Furthermore, the coated polymer film obtained as an intermediate product is likely to harden with time in the preservation in the roll form with a considerably small speed. The hard coat layer cannot have a constantly expected hardness at the time of coating of the anti-reflection layer.